Liquid chromatography is used in many industries to purify chemical and biological compounds for analytical and preparative purposes. In liquid chromatography, as well as in other liquid-handling endeavors such as microfluidics, control of dissolved gas concentrations is a prerequisite to accurately metering liquids, detecting species of interest, and separating these species from contaminants. Dissolved gases, in particular O2, can react with species of interest, the liquids carrying these species, and the media (e.g. tubing, chromatography columns) through which these species pass, complicating purification procedures. Gases can also absorb light and interfere with the optical detection of a species in a liquid stream. These problems are made more acute by outgassing, the phenomenon of dissolved gases precipitating out of solution due to, for example, a drop in liquid pressure, an increase in temperature, or a change in solution composition.
Known methods of reducing gas concentrations in liquids include, for example, sparging and vacuum degassing. Sparging involves bubbling a weakly soluble gas such as helium through a liquid, thereby displacing and expunging more soluble gases such as O2 from the liquid. Vacuum degassing involves applying a vacuum to the liquid, such as by evacuating the space above the liquid or drawing a vacuum against a gas-permeable membrane with which the liquid is in contact. In the presence of the vacuum, the solubility of gas in the liquid will fall according to Henry's law, and gas will escape the liquid. Degassing strategies are discussed in Bakalyar et al., J. Chromatography 158, 277-293, 1978, in Snyder et al., Introduction to Modern Liquid Chromatography, 3rd ed., New York: Wiley, 2010, and elsewhere.
These methods are labor intensive and, in the case of vacuum degassing, require an external vacuum source and proper sealing of the space adjacent to the liquid, among other factors.